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Must Star-forming Galaxies Rapidly Get Denser before They Quench?
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| Zeitschriftentitel: | The Astrophysical Journal |
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| Personen und Körperschaften: | , |
| In: | The Astrophysical Journal, 858, 2018, 1, S. 40 |
| Format: | E-Article |
| Sprache: | Unbestimmt |
| veröffentlicht: |
American Astronomical Society
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| Schlagwörter: |
| Zusammenfassung: | <jats:title>Abstract</jats:title> <jats:p>Using the deepest data yet obtained, we find no evidence preferring compaction-triggered quenching—where rapid increases in galaxy density truncate star formation—over a null hypothesis in which galaxies age at constant surface density (<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}\equiv {M}_{* }/2\pi {r}_{e}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). Results from two fully empirical analyses and one quenching-free model calculation support this claim at all <jats:italic>z</jats:italic> ≤ 3: (1) qualitatively, galaxies’ mean <jats:italic>U</jats:italic>–<jats:italic>V</jats:italic> colors at <jats:inline-formula> <jats:tex-math> <?CDATA $6.5\,\lesssim \mathrm{log}{{\rm{\Sigma }}}_{e}/{\text{}}{M}_{\odot }\,{\mathrm{kpc}}^{-2}\lesssim 10$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn2.gif" xlink:type="simple" /> </jats:inline-formula> have reddened at rates/times correlated with <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, implying that there is no density threshold at which galaxies turn red but that <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn4.gif" xlink:type="simple" /> </jats:inline-formula> sets the pace of maturation; (2) quantitatively, the abundance of <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{* }/{\text{}}{M}_{\odot }\geqslant 9.4$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn5.gif" xlink:type="simple" /> </jats:inline-formula> red galaxies never exceeds that of the total population a quenching time earlier at any <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn6.gif" xlink:type="simple" /> </jats:inline-formula>, implying that galaxies need not transit from low to high densities before quenching; (3) applying <jats:inline-formula> <jats:tex-math> <?CDATA $d\mathrm{log}{r}_{e}/{dt}=1/2\,d\mathrm{log}{M}_{* }/{dt}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn7.gif" xlink:type="simple" /> </jats:inline-formula> to a suite of lognormal star formation histories reproduces the evolution of the size–mass relation at <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{* }/{\text{}}{M}_{\odot }\geqslant 10$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn8.gif" xlink:type="simple" /> </jats:inline-formula>. All results are consistent with evolutionary rates being set ab initio by global densities, with denser objects evolving faster than less-dense ones toward a terminal quiescence induced by gas depletion or other ∼Hubble-timescale phenomena. Unless stellar ages demand otherwise, observed <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{e}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab61bieqn9.gif" xlink:type="simple" /> </jats:inline-formula> thresholds need not bear any physical relation to quenching beyond this intrinsic density–formation epoch correlation, adding to Lilly & Carollo’s arguments to that effect.</jats:p> |
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| Umfang: | 40 |
| ISSN: |
0004-637X
1538-4357 |
| DOI: | 10.3847/1538-4357/aab61b |